Our interest in the phagocyte- and tumor cell-derived protein MFG-E8 continues. We have generated several MFG-E8 mouse mutants to determine if MFG-E8 has a role tumor biology and immunophysiology in vivo. Results, to date, indicate that tumor cells produce MFG-E8 and that MFG-E8 promotes tumorigenesis in both orthotopic and transgenic models of cancer in mice (melanoma, non-melanoma skin cancer, colon cancer and pancreatic beta-cell cancer). In addition, ongoing experiments suggest that MFG-E8 may be a relevant therapeutic target in cancer. In collaboration with Dr. James Mitchell of the CCR's Radiation Branch, we are attempting to incorporate MFG-E8 related proteins into a tumor vaccine approach that will also involve utilization of radiation therapy and chemotherapy in several mouse models of cancer. In an effort to elucidate mechanisms by which MFG-E8 modulates tumor formation, we are also studying several mouse models of leukocyte recruitment. These studies are being carried out in collaboration with Dr. Trian Chavakis of the CCR's Experimental Immunology Branch. In his laboratory, Dr. Chavakis has been studying the MFG-E8 homolog Del1, and has elucidated an unexpected role for Del1 in neutrophil recruitment. The involvement of MFG-E8 leukocyte recruitment would provide a mechanism by which this protein could either enhance or inhibit tumorigenesis, and this area of investigation is being actively pursued. To gain additional understanding of the roles that MFG-E8 plays in tumor formation and immunophysiology, we are carefully localizing MFG-E8 accumulation in vivo in tumors and in normal tissues. Utilizing highly specific affinity-purified polyclonal antibodies, we have determined that MFG-E8 is found focally in vascular or perivascular locations and in other specific locations as well. In the past year, we have documented that, in tumors, pericytes produce more MFG-E8, on a per cell basis than leukocytes, endothelial cells and tumor cells. We hypothesize that pericyte-derived MFG-E8 regulates endothelial cell function and are testing this hypothesis in several in vitro and in vivo models. We further hypothesize that MFG-E8 mat represent a valid therapeutic target in diseases in which unwanted angiogenesis is a critical factor.